This invention relates to apparatus for combining or dividing high frequency power. More particularly, this invention relates to apparatus for combining the outputs of serially connected high frequency power sources or for dividing high frequency power into serially connected loads.
In the past, high frequency power, such as rf or microwave power has been combined or split using coaxial T's or hybrid T's. These three port devices may or may not be impedance matched at each port, but all are intended for use with sources and loads having a common reference potential. While such devices are adequate to combine or split high frequency power when the sources and loads have a common reference potential, coaxial T's or hybrid T's are not useful for combining the outputs of serially connected high frequency power sources.
Since microwave transistors, diodes, and other solid state devices are inherently low voltage devices, it has been common practice to employ transformers to step down the 60 Hz ac line voltage to a level compatible with these microwave devices. Transformers suitable for use at 60 Hz are heavy, bulky, and expensive and are generally undesirable in high frequency power sources used in microwave appliances, communicaton systems and electrodeless light sources. However, when standard 60 Hz ac line voltage is rectified without the use of a transformer, the resulting voltage is well above 100 volts. One approach to operation without a transformer is to connect two or more high frequency devices in series across the high voltage thereby reducing the voltage applied to the individual devices. For example, two high frequency transistor oscillators can be connected in series across line voltage which has been rectified and filtered. The voltage applied to each oscillator and hence to each high frequency transistor is one half the total voltage. The series connection, however, results in two or more outputs, each having a different dc potential. It is necessary, therefore, to provide an apparatus for combining the outputs of the serially connected power sources.